The present invention relates to optical signal transmission and, more specifically, an improved optical waveguide useful in applications requiring modulation and switching of optical signals.
It is becoming increasingly important to frequently upgrade telecommunication networks to increase their capacity due to the recent rapid increase in network traffic caused by multimedia communications. Although optical technologies are replacing most transmission lines, the nodes of optical networks, such as switching and cross-connect nodes, still depend on relatively slow electrical technologies. Specifically, time-division multiplexing (TDM) systems are widely used in existing optical communications systems and are inherently dependent on electrical circuits for multiplexing and demultiplexing. As a result, the electrical nodes in these types of optical networks limit throughput.
Accordingly, there is a need in the art for advances in telecommunication network design. More specifically, there is a need for innovation in the areas of switching, modulation, multiplexing and demultiplexing via optical technologies.
This need is met by the present invention wherein waveguides and integrated optical devices incorporating optically functional cladding regions are provided. A significant advantage of many embodiments of the present invention lies in the use of two or more electrooptic cladding regions that are, through appropriate poling and/or deposition procedures, oriented with their polar axes in different directions. This type of orientation and variations thereof, as described herein, allow for production of waveguides and integrated optical devices exhibiting unique functionality and allowing for optimum flexibility in device design. The waveguides and integrated optical devices described herein may be exploited in various ways, many of which are described herein.
In accordance with one embodiment of the present invention, an electrooptic clad waveguide is provided comprising an optical waveguide core and first and second cladding regions. The optical waveguide core defines a primary axis of propagation z. The first cladding region is offset from the z axis in a first direction along an x axis perpendicular to the z axis. The second cladding region is offset from the z axis in a second direction along the x axis. The optical waveguide core comprises a substantially non-electrooptic material defining a refractive index n1 and the first and second cladding regions comprises an electrooptic polymer defining a refractive index that is less than n1. The first and second cladding regions may be poled in opposite or perpendicular directions.
In accordance with another embodiment of the present invention, an electrooptic clad waveguide is provided where first and second control electrodes are arranged to enable electrooptic modification of the refractive indices of the first and second cladding regions by creating a contoured electric field in the first and second cladding regions. The contoured electric field and the respective directions of polarization in the first and second cladding regions define a polarization-independent waveguide structure along the primary axis of propagation of the electrooptic clad waveguide. Preferably, the first and second cladding regions are poled along substantially the same contour of the electric field.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided comprising an optical input, an optical output, an electrooptic clad waveguide, and first and second control electrodes. The electrooptic clad waveguide is arranged along an optical path defined between the optical input and the optical output. The electrooptic clad waveguide is characterized by an optical phase delay xcfx86=2xcfx80Lneff/xcex, where neff is the effective index of refraction of the waveguide, L is the length over which the phase delay occurs, and xcex is the wavelength of light propagating along the optical path. The electrooptic clad waveguide comprises an optical waveguide core defining a primary axis of propagation z, a first cladding region offset from the z axis in a first direction along an x axis perpendicular to the z axis, and a second cladding region offset from the z axis in a second direction along the x axis. The optical waveguide core comprises a substantially non-electrooptic material defining a refractive index n1. The first and second cladding regions comprise an electrooptic polymer defining a refractive index that is less than n1. The waveguide core defines a cross-sectional x axis width that decreases from a region outside of the first and second cladding regions to a region bounded by the first and second cladding regions. The first and second control electrodes are arranged to create an electric field in the first and second cladding regions capable of changing the refractive indices of the first and second electrooptic cladding regions without a corresponding change in the refractive index n1 of the waveguide core so as to induce a core-independent change in neff and a corresponding change in the optical phase delay xcfx86 of the waveguide.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided where first and second waveguides are arranged to define a Mach-Zehnder interferometer. The interferometer includes first and second directional coupling regions, an intermediate coupling region disposed between the first and second directional coupling regions, a set of control electrodes, an optical input, and at least one optical output. One or both of the first and second waveguides comprise an electrooptic clad waveguide comprising a substantially non-electrooptic optical waveguide core defining a refractive index n1. The waveguide core of the electrooptic clad waveguide is disposed between first and second cladding regions in the intermediate coupling region. The first and second cladding regions comprise a poled electrooptic polymer defining a refractive index that is less than n1. The control electrodes are arranged to create an electric field in the first and second cladding regions capable of changing the refractive indices of the first and second electrooptic cladding regions so as to induce a change in an effective index of refraction neff of the electrooptic clad waveguide. The control electrodes are further arranged so that a quantitative combination of the electric field and the poling in the first cladding region is substantially equivalent to a quantitative combination of the electric field and the poling in the second cladding region. In this manner an output intensity Iout at one of the optical outputs is related to an input intensity Iin according to one of the following equations       |          I      out        ⁢          |      2        =            |              I        in            ⁢              |        2            ⁢                        sin          2                ⁡                  (                      φ            2                    )                    ⁢              
            |              I        out            ⁢              |        2              =          |              I        in            ⁢              |        2            ⁢                        cos          2                ⁡                  (                      φ            2                    )                    
where xcfx86 represents optical phase delay resulting from the change in the effective index of refraction neff of the electrooptic clad waveguide.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided comprising first and second electrooptic clad waveguides arranged to define a Mach-Zehnder interferometer. The interferometer includes first and second directional coupling regions, an intermediate coupling region disposed between the first and second directional coupling regions, a set of control electrodes, first and second optical inputs, and first and second optical outputs. The waveguide core of the first waveguide is disposed between first and second cladding regions of the first waveguide in the intermediate coupling region. The waveguide core of the second waveguide is disposed between first and second cladding regions of the second waveguide in the intermediate coupling region. The poling of the first and second cladding regions of the first waveguide is substantially perpendicular to the poling of the first and second cladding regions of the second waveguide. The control electrodes are arranged to create an electric field in the first and second cladding regions of the first and second waveguides to induce a change in an effective index of refraction neff of the first and second waveguides, whereby input optical signals may be directed selectively to separate ones of the optical outputs by controlling the electric field.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided comprising first and second waveguides arranged to define a Mach-Zehnder interferometer. The control electrodes of the device form a traveling wave stripline and are arranged to create an electric field in the first and second cladding regions capable of changing the refractive indices of the first and second electrooptic cladding regions so as to induce a change in an effective index of refraction neff of the electrooptic clad waveguide. The traveling wave stripline is characterized by a dielectric constant xcex5 selected such that an optical signal propagating in the electrooptic clad waveguide propagates at the same velocity as an electrical signal propagating in the traveling wave stripline. The control electrodes are arranged such that a quantitative combination of the electric field and the poling in the first cladding region is substantially equivalent to a quantitative combination of the electric field and the poling in the second cladding region, whereby an output intensity Iout at one of the optical outputs is related to an input intensity Iin according to one of the following equations       |          I      out        ⁢          |      2        =            |              I        in            ⁢              |        2            ⁢                        sin          2                ⁡                  (                      φ            2                    )                    ⁢              
            |              I        out            ⁢              |        2              =          |              I        in            ⁢              |        2            ⁢                        cos          2                ⁡                  (                      φ            2                    )                    
where xcfx86 represents optical phase delay resulting from the change in the effective index of refraction neff of the electrooptic clad waveguide.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided comprising first and second electrooptic clad waveguides of unequal length arranged to define an asymmetric Mach-Zehnder interferometer. The control electrodes are arranged to create an electric field in the first and second cladding regions of the first and second waveguides to induce a change in the effective index of refraction neff of the first and second waveguides. In this manner, first and second wavelength components of an input optical signal may be directed selectively to separate ones of the optical outputs by controlling the electric field.
In accordance with yet another embodiment of the present invention, an integrated optical device is provided comprising first and second electrooptic clad waveguides arranged to define a directional coupling region. The waveguide core of the first waveguide is disposed between a first outer electrooptic cladding region and an electrooptic gap region in the directional coupling region. The waveguide core of the second waveguide is disposed between a second outer electrooptic cladding region and the electrooptic gap region in the directional coupling region. The control electrodes are arranged to create an electric field across the outer cladding regions and the electrooptic gap region, whereby an optical signal incident in one of the waveguides may be switched to the other of the waveguides.
In accordance with yet another embodiment of the present invention, an optical waveguide is provided comprising a waveguide core defining a core height dimension h that remains substantially constant between the optical input and the optical output. The core width dimension defines an input width w1 at the optical input, an output width w2 at the optical output, an increased-width w0 along a phase compensating element of the waveguide core, and a decreased-width w3 along a thinned-down portion of the waveguide core. The increased-width w0 is greater than the input width and the decreased-width w3 is less than the input width.
In accordance with yet another embodiment of the present invention, an optical waveguide is provided where the core width dimension defines an increased-width w0 along a phase compensating element of the waveguide core and a decreased-width w3 along a thinned-down portion of the waveguide core. The decreased-width w3 is less than the core height dimension h and the increased-width w0 is greater than the core height dimension h.
In accordance with yet another embodiment of the present invention an integrated optical device is provided comprising a plurality of channel waveguides and a thermo/electric poling arrangement. At least a pair of the waveguides are at least partially bounded along a portion of their length by respective electrooptic cladding regions defining respective polar axes. The thermo/electric poling arrangement is provided proximate the respective electrooptic cladding regions and is arranged to orient independently the respective polar axes of the cladding regions.
Accordingly, it is an object of the present invention to provide improved optical waveguides and integrated optical devices useful in applications requiring modulation and switching of optical signals. Other objects of the present invention will be apparent in light of the description of the invention embodied herein.